When supplying energy to electronic circuits which require relatively high output, DC/DC converters should increase their output voltage to be utilized in specific applications Dependent upon the load, the DC/DC converter may need to slowly decrease the output voltage. For this, a DC/DC converter is one of various voltage-lowering and voltage-boosting converters.
Meanwhile, currently, along with a tendency for worldwide Green Growth Policy, electronic vehicles (EV) represents a future converging technology to which there is a growing attention from not only international organizations but also governments and enterprises in each country.
Provided with electric power from outside and charging to a battery, such electronic vehicles obtain power, which is mechanical energy, using voltage charged to the battery. As an apparatus for providing the voltage which electronic vehicles require for charging low voltage and high voltage, a charger for vehicles needs a DC/DC converter which enables to provide outputs of a wide voltage range of direct current power source from direct current input power source by using a single output circuit.
Such DC/DC converter has been disclosed in Korean Registration Patent no. 10-1548528 (DC/DC converter).
The DC/DC converter comprises a switching unit for switching direct current input power source alternately; a voltage transformer for converting power source switched by the switching unit, containing a single trans which includes a primary winding and a secondary winding, converting the power source inputted in the primary winding, and outputting to the secondary winding; a rectification unit for rectifying alternating current power supply, outputted in the secondary winding of the voltage transformer, to direct current power source, containing a switching element and first to fourth diodes, and operating using a high voltage mode or a low voltage mode in accordance with operation of the switching element; and an output filter for filtering power source outputted from the rectification unit, wherein the rectification unit refers to a bridge rectification circuit which comprises, in the high voltage mode, the first diode and the second diode each connected in forward direction to both ends of the secondary winding of the voltage transformer, and the third diode and the fourth diode each connected in reverse direction to both ends of the secondary winding of the voltage transformer; wherein the rectification unit refers to a center-tapped rectification circuit which comprises, in the low voltage mode, the first diode and the second diode each connected in forward direction to both ends of the secondary winding of the voltage transformer, and a center tap formed in the secondary winding of the voltage transformer and connected to a connection terminal; and wherein the switching element of the rectification unit includes a first switch which turns on/off between the center tap and the connection terminal and a second switch which turns on/off between negative poles of the third diode and the fourth diode and the connection terminal; and wherein the first switch turns off in the high voltage mode and turns on in the low voltage mode and the second switch turns on in the high voltage mode and turns off in the low voltage mode.
Further, the DC/DC converter consists of a full-bridge converter, or a half-bridge converter, or a push-pull circuit to generate alternating voltage with input DC voltage switched alternately.
However, the DC/DC converter halves a number of the secondary winding of a trans and uses depending on a size of an output voltage for supplying outputs of a wide voltage range, i.e., using the secondary winding as one winding as for low output voltage, and the secondary winding of the trans as two windings in series as for high voltage. There is a current, which requires for output, flowing in the winding and thus, the current constantly flows even as for using one trans winding and two trans windings in series. Thus, there needs to select a diameter of the winding for allowing two windings in the maximum output current. At this time, there is a problem that a size of the trans becomes large for obtaining a space to coil up two windings as compared to using thick winding as a single winding.
In addition, upon high voltage output, two windings of the trans are connected in series, thereby applying double higher voltage rating to the second diode and requiring to use high voltage rating of diode. There is a problem that high pressure resistant diode has high voltage forward (VF), thereby incurring loss.
Furthermore, in the common quick charger, high voltage and current are generated when charging with a high capacity, and loss is reduced in case that current is smaller than voltage. Thus, it needs to increase voltage for flowing small current. In general circuit methods, in case for applying high voltage so as to reduce current, it is not possible to use general MOSFET with available cost and supply, because high voltage is generated in the switch element, and there is a problem that loss is incurred due to large current flow when reducing input voltage so as to use MOSFET.